In this letter, we present a deformable mirror (DM) which consists of a square flexible membrane with photoresist-defining circle of 25mm diameter actuated by electrostatic force using an array of 67 hexagonal electrodes. To achieve the goal of correcting wavefront aberrations in optical system with lower voltage, we fabricate a low residual stress membrane by using polyimide. We develop it to sandwich structure due to coefficient of thermal expansion mismatch consideration. The maximum deflection is 34-&#956;m at the center of membrane. Furthermore, we use the finite element method (FEM) to simulate DM for predicting the membrane deflection.

Shack-Hartmann wavefront sensor based on USB camera: what is bad and what is good?
Paper 7816-20
Author(s):

Knowledge of key parameters of optical turbulence is essential for prediction of optical performance in both imaging and transmitting applications. The basic parameters are r0, the Fried coherence length, and fG, the Greenwood frequency. Other measures, such as inner scale and temporal variation of turbulence strength, are also important to assess adaptive optics performance in detail. We illustrate techniques to estimate r0, fG, and inner scale from Shack Hartmann wavefront sensor measurements that are sufficiently accurate to estimate changes in turbulence strength over short time intervals. Results from several field campaigns with a 32x32 Hartmann sensor will be presented.

The Large Synoptic Survey Telescope is designed to map out the dark matter in the universe. This telescope will require active correction of its mirrors to remove the aberrations that arise from changing gravitational force vectors and from thermal drifts during observational runs. In this presentation we present an evaluation of a Shack-Hartmann wavefront sensor and reconstruction algorithm which is capable of meeting the challenges associated with this wide field-of-view survey telescope. The advantages of this technique over other potential technologies are discussed and the potential problems encountered with this approach are analyzed and solutions to these problems presented.

In earlier work we have shown that pupil plane branch points carry information about the conditions of the
atmospheric turbulence. Experiments in the Atmospheric Simulation and Adaptive-optic Laboratory Test-bed
(ASALT) at the Air Force Research Laboratory, Directed Energy Directorate's Starfire Optical Range have
shown that branch points can provide the number and velocity of turbulence layers. Here we demonstrate that
these measurements can further be used to estimate the turbulence layers' altitude and strength. This work is
the culmination of research demonstrating that a methodology exists for identification of the number, altitude,
strength, and velocity of atmospheric turbulence layers.

We propose a sensor to be used to optimize a multi-conjugate adaptive optics system that calculates the number, strength, altitude, and velocity of atmospheric turbulence layers using measurements of branch point separation, velocity and density. Though branch points are not commonly present in astronomical data, artificially increasing the propagation distance with an optical trombone creates branch points in atmospheric regimes where branch points do not form. Here we present the design for a sensor that creates and measures branch points and characterizes the atmospheric turbulence layers, as well as data demonstrating the implementation, limitations and hardware trade-offs of this sensor.

The ASALT lab has been investigating the use of a segmented MEMS DM in adaptive optics systems. Here, we investigate the fitting error for a segmented deformable mirror with flat subaperture segments. This investigation is done in the regime where the hidden phase is significant. Data from both simulation and experiment are presented, giving initial estimates of the magnitude of the error.

Micro-Electro-Machined Systems (MEMS) have been increasingly used as mirrors in place of conventional continuous phase sheet deformable mirrors (DM) in adaptive optics (AO) systems. Here we study the diffraction effects introduced into the optical path when a segmented MEMS DM is used. Two optical layouts directing the beam from the MEMS mirror to the self referencing interferometer are compared, one having apparent diffraction effects, and another one with such effects intentionally removed. AO system closed loop performance is compared and analyzed for both cases.

Phase compensation instability (PCI) is the time-dependent development of spatial perturbations that occur within thermally bloomed high-energy laser (HEL) beams. This study uses a straightforward wave-optics code to model horizontal propagation with the effects of thermal blooming for a focused Gaussian beam. A nominal adaptive-optics system is used to mitigate phase distortions accumulated from thermal blooming. Parameters within the adaptive optics system, such as the number of actuators on the deformable mirror and the resolution of the wavefront sensor, are varied to determine the impact of spatial resolution in the development of PCI.

We will develop and then compare object spectrum phasor reconstruction results for several speckle imaging approaches. Each phasor reconstruction algorithm results from minimizing a very naturally defined weighted-least-squares error function. Once we pick a phasor-based error function, the remaining steps in our algorithms are developed by setting the error function variation, with respect to each phasor element, to zero. The resulting coupled nonlinear equations for the minimum error phasor array are then solved iteratively. In the applications, we will compare and contrast three implementations: 1) Knox-Thompson (KT); 2) Bispectrum, using only two bispectrum planes, (TCA); 3) Bispectrum, using four bispectrum planes, (TCB). In each application of the three approaches, we first calculate the modulus of the object spectrum using a Wiener-Helstrom filter to remove the speckle transfer function. The methods then differ only in their object spectrum phasor reconstructions.

Adaptive jitter control for tracker line of sight stabilization
Paper 7816-21
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A field test experiment on a range tracking telescope at the U. S. Army White Sands Missile Range, is exploring the use of recently developed adaptive control methods to minimize track loop jitter. Gimbal and platform vibration are the main sources of jitter in the experiments, although atmospheric turbulence also is a factor. In initial experiments, the adaptive controller reduced the track loop jitter significantly in frequency ranges beyond the bandwidth of the existing track loop. This paper presents some of the initial experimental results along with analysis of the performance of the adaptive control loop. The paper also describes the adapative control scheme, its implementation on the WSMR telescope and the system identification required for adaptive control.

Polymer membrane deformable mirrors offer a low-cost alternative to conventional technology in a wide variety of adaptive optics or laser beam shaping applications. In this paper we evaluate the suitability of two different kinds of polymer membrane deformable mirrors for laser machining. We begin by presenting results from a demonstration of a new compact laser beam shaping system using a polymer membrane deformable mirror. We evaluate the effect of Q-switched laser radiation on polymer membranes at 355nm and 1060nm. We conclude with a comparison of the material properties of the two materials relative to the needs of laser machining.

The Naval Research Laboratory (NRL) has developed a new method for generating atmospheric turbulence and a testbed that simulates its aberrations far more inexpensively and with greater fidelity using a Liquid Crystal (LC) Spatial Light Modulator (SLM) than many other methods. This system allows the simulation of atmospheric seeing conditions ranging from very poor to very good and different algorithms may be easily employed on the device for comparison. These simulations can be dynamically generated and modified very quickly and easily. In addition, many models for simulating turbulence often neglect temporal transitions along with different seeing conditions.

Iris AO has been developing a 489-actuator, 163 piston-tip-tilt (PTT) segment, deformable mirror system controlled with a personal computer. The system includes the MEMS-based DM, drive electronics, and a factory-calibrated open loop position controller. The position controller implements both position limiting to keep DM segments within the safe operating region and calculates the actuator voltages that correspond to DM piston, tip, and tilt positions.
This paper will describe recent speed enhancements and benchmarking results for the 489-actuator deformable mirror system. It presents all aspects that give rise to latencies and frequency response, namely: 1) PTT controller safe-operating-point limiting and voltage calculations; 2) computer interface latencies and DAC slewing, and 3) DM frequency response.

We introduce and demonstrate a new quasi-ternary nonmechanical beam steering design based on Polarization Gratings (PGs). This design uses a single wave-plate and N PGs to generate 2^(N+1)-1 steering angles. When compared with conventional designs, this technique uses fewer elements arranged in a simpler configuration to achieve the same number of steering angles. The design is based on adapting the unique properties of PGs that can diffract with ~100% efficiency into a single order depending upon the polarization. Using this approach we demonstrate a beam steering device that achieves ~80&#730; field of regard with ~4&#730; resolution at 1550 nm wavelength.

An experimental study showing the effects on a standard PI controller using a segmented MEMS DM acting as a mod(λ) device
Paper 7816-15
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The ASALT lab has been investigating the use of a segmented MEMS DM in adaptive optics systems. One of the anticipated benefits of a segmented device is that in monochromatic light the throw is infinite because of the modulo 2pi nature of the device. Earlier work demonstrated how this modulo pi behavior interacts unexpectedly
with a standard proportional integral controller. Here we present experimental data on this effect to include the
testbed on which the data was taken and the methodology used to measure the effect.

The concept of the laser guide star was proposed by Foy and Labeyrie, 1985. The Laser Guide Stars (LGS) depend on the abundance and distribution of sodium in the mesosphere. The mesopheric sodium often appears to consist of more than one layer, each of which exhibits time variation in density and altitude. The non-zero thickness and finite range of the layers results in elongation of the LGS defocus on extremely large telescopes such as TMT and VLT. Na variability will be examined for determination, analysis and impact on Adaptive Optics aberration correction.

SWIR air glow mapping of the night sky
Paper 7816-17
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It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between 0.9 and 1.7 um wave length. Numerous studies of these phenomena have demonstrated that the irradiance shows significant temporal and spatial variations. Changes in weather patterns, seasons, sun angle, moonlight, etc have the propensity to alter the SWIR air glow irradiance pattern. By performing multiple SWIR measurements a mosaic representation of the celestial hemisphere can be constructed and used to investigate the variations over time and space. Measurements are presented for NM and Maui.

It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between 0.9 and 1.7 um wave length. Spatio-temporal variations of the sky glow manifest themselves as traveling wave patterns whose period and velocity are related to the wind velocity at 85 km as well as the turbulence induced by atmospheric vertical instabilities. In this paper we propose the use of sky glow observations to predict and characterize image system degradation due to upper atmosphere turbulence.